Older versions of iChat not working in IM policy

FortiGate

FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.

Article Id 195981

Description
Problems may be encountered using the iChat instant messenger client, this is quite common with older versions of the iChat client.

In FortiOS 3.0 the only supported Instant Message software are AIM, MSN, Yahoo! and ICQ. iChat is not directly supported. By default iChat fails the version check performed by the FortiGate.
Reference

Workaround

There is a CLI command to enable the FortiGate to do a best effort to attempt with older AIM versions. This will allow iChat to login and send messages. However this not allow sending files or video chat or use any of the other iChat features beyond sending messages.

From FortiGate Command line (or console in the GUI) run the following commands:

#config imp2p old-version
#set aim best-effort
#end

745

Broad. Integrated. Automated.

The Fortinet Security Fabric brings together the concepts of convergence and consolidation to provide comprehensive cybersecurity protection for all users, devices, and applications and across all network edges.